C57BL/10 (#:000476), mdx mice (C57BL/10ScSn-Dmdmdx/J) (#:001801) and mdx mice in the DBA2/J background (D2-mdx) (#:013141) were obtained from The Jackson Laboratory. CD45.1 congenic mice (#:002014) were also obtained from The Jackson Laboratory and crossed with mdx mice at the University of California Irvine (UCI). B6A/J (#:012767) and C57BL/6 mice (#:000664) were bred in vivariums at Children’s National Hospital. VCP (53 (link)) and DUX4 (54 ) mice were provided by collaborators at UCI and Ohio State University, respectively. Animal experiments were approved by the Institutional Animal Care and Use Committee of UCI.